The present invention relates to an electrophotographic recording material comprising an electrically conductive base material and at least one photoconductive layer containing a photoconductor and 3,3'-dimethylindolenine sensitizing dyes.
In electrophotographic reproduction, it is known to use photoconductors that are sensitive to radiation in the short-wave visible portion of the spectrum. It is also known that the radiation-sensitivity of such photoconductors in the visible portion of the spectrum can be extended by addition of one or more sensitizing dyes capable of transferring the energy of longer-wave light to the photoconductor. Various classes of dye compounds can be used for sensitization of photoconductors in this manner.
It is known (see German Auslegeschrift No. 2,526,720, corresponding to U.S. Pat. No. 4,063,948) to use in electrophotographic reproduction an electrophotographic recording material that contains, in the photoconductive layer, a cyanine dye which has a sensitizing action in the blue spectrum. However, such a sensitizing action does not make it possible also to record, for example, radiation in the green and red parts of the spectrum.
It is also known (see German Offenlegungsschrift No. 1,447,907, corresponding to U.S. Pat. No. 3,458,310) to sensitize photoconductor layers to the visible red portion of the spectrum. This is done by using, for example, mixtures of acridine yellow, acridine orange, rhodamine dye and brilliant green which are added in one layer or separately, in different layers (see German Offenlegungsschrift No. 2,353,639, corresponding to U.S. Pat. No. 3,992,205), when the respective sensitization actions of individual dyes are added together or, alternatively, the resultant actions are different (see German Offenlegungsschrift No. 2,817,428, corresponding to U.S. Pat. No. 4,252,880).
Such panchromatic sensitizations provide advantages to the extent that high-red light sources used in reproduction technology are better utilized. In practice this means shorter exposure times and, hence, time and energy savings. Due to improved sensitivity, it is also possible to reduce the photoconductor content in the photoconductive layer.
Since one sensitizer alone generally does not cover the entire visible spectrum, it is necessary to mix more than one sensitizer. But it is very difficult thereby to obtain sensitizations that meet the varied requirements of the reproduction industry. Different sensitizers, with differing chemical as well as absorptive properties, must nevertheless be soluble in the solvent used and in the binding agent of the photoconductive layer. Different sensitizers used in a mixture may also influence each other in such a way as to affect adversely the sensitizing properties of the mix.